For this year’s Mostly Mozart Festival, Mark Morris stayed off the stage and climbed into the orchestra pit.

And what’s coming out of there — where Morris conducts the festival orchestra, the Trinity Choir and five marvelous soloists — is the best part of his staging of “Dido and Aeneas,” which opened Wednesday night.

The tale of Henry Purcell’s 17th-century British opera is loosely taken from Virgil’s “Aeneid.” Here, Aeneas woos Dido, queen of Carthage, but their happiness is thwarted by an evil sorceress, who tricks Aeneas into abandoning his love.

When Morris first staged the opera in 1989 for his Brussels troupe, he played both female leads. Those performances were the stuff of legend — people thought the ballet couldn’t be revived without him.

But now those roles are again danced by a woman, Amber Star Merkens, who goes over the top to fill Morris’ outsized dancing shoes. She poses and glares, lying down in spasm and shaking her silver nails.

It’s forceful, but looks lifted from “Victor/Victoria” — like a woman imitating a man imitating a woman.

Her Aeneas, Domingo Estrada Jr., is small, dark and handsome, but Morris’ choreography keeps them at arm’s length. The real chemistry relies on the marvelous voices intertwining from the pit.

Morris’ great skill is creating the kaleidoscope of shifting patterns as lines of dancers sift forward or spread across the stage. Yet the simple faux-antique moves — hop, step, stamp, pose — become one Grecian urn too many. And when his dancers act out the lyrics, it can be as obvious as a “Silly Symphony” cartoon.

The simple décor works: a few railings in front of a dropcloth that looks like an abstracted map of ochre islands adrift in a turquoise sea. But when the dancers, clad in plain black shmattes, play more than one role without a costume change, it’s confusing.

Still, what singing! The title couple is voiced luminously by mezzo Stephanie Blythe and baritone Joshua Jeremiah. Blythe’s soaring, gripping rendition of Dido’s final lament, “When I am laid in Earth” is like a divine wind that engulfs the stage — even if she’s not on it.

Take Balanchine’s famous advice: If you don’t like the dancing, close your eyes.